There is little doubt now that haplogroup G was one of the main lineages of the people who spread agriculture from the Levant to the Middle East and Europe. Early farming arose in the Levant, and the highest genetic diversity for haplogroup G is also found in the Levant. The odd thing is that hg G is remarkably sparse in the region today: only around 3 or 4%, except in Lebanon where it is a little bit higher (6.5%), but still nowhere like a major local haplogroup. In contrast, Ashkenazi Jews have 10% of G, and Sephardic Jews 15%. Since the Jewish diaspora took place about 2000 years ago, before the Arabic conquest of the Middle East, it would make sense to think that the percentage of hg G was considerably higher in the southern Levant 2000 years ago than today. So did the Arabs cause haplogroup G to contract at least three times and perhaps as much as five fold ?
In modern Palestine, haplogroup J1 makes up about 40% of the lineages, twice more than among the Jewish community. Since J1 is strongly associated with the Arabic expansion, it is reasonable to assume that at least a fifth of the lineages in the region were taken over by the Arabs. The Arabs surely also carried haplogroups E1b1b and T, common on the Red Sea coast of Arabia, and which are slightly higher among Palestinians than among the Jews. So we could assume that approximately 25% of Palestinian lineages today came with the Arabs during the Muslim conquest.
It makes sense when looking at other haplogroups like J2 and R1b, but it still doesn't explain the sharp drop experienced by haplogroup G from 10-15% to 3%. It could be that G was considerably more common among the Jews of the diaspora, which caused a sort of founder effect.
But then why was G so ubiquitous in all Neolithic sites tested so far ? Europe has been affected as much by the sharp decline of G as the Levant. What other factors could have caused a gradual decrease of G since the Neolithic ? Were G men more frequently the victims of foreign invasions because they had settled the fertile Mediterranean lands first ? Each invasion in the last 9000 years would have progressively reduced the proportion of the original Neolithic farmers as new people settled in. But then why hasn't E1b1b, which also spread agriculture from the Neolithic Levant, undergone the same decline ?
Another possibility is that the G Y-chromosome produces slightly less male offspring than other haplogroups. I theorised five years ago that the exceptionally wide distribution of haplogroup R1b (and in fact also R1a) was due in part to a genetic bias towards producing slightly more male children. It doesn't take much to achieve this over hundreds of generations. If haplogroup R1 produced just 1% more boys than other haplogroups in average, R1 would increase its proportion 7.4 folds after the roughly 200 generations since the presumed arrival of R1b in Western Europe 6000 years ago.
In other words, if a population was composed of 100 R1b men and 100 men belonging to other haplogroups, if R1b men fathered 101 boys each generation, but other haplogroups kept a stable 100, it would take only 70 generations (about 2000 years) for R1b men to reach 200 boys born each generation, and therefore double their proportion against other haplogroups. The R1b frequency would thus pass from 50% to 66.6%. After 200 generations (about 6000 years), there would be 738 R1b boys against 100 other boys born at each generation. R1b would now make up 88% of the lineages in that population. As you can see a very minor initial advantage can lead to enormous changes in frequencies after a few millennia. Western Europe now has about 60% of R1b in average. With a bias of 1% more boys per generation, it would have taken an initial population of less than 10% of R1b 6000 years ago to reach that modern proportion.
If haplogroup G had the opposite bias, and produced 1% less boys than men belonging to other haplogroups, its proportion would gradually decline without any other factor required. If a given Neolithic population had 50% of hg G, with a bias of -1% of boys per generation against other haplogroups, it would have taken about 7000 years for the proportion of G to naturally decline to only 5% of the population.
If we combine both the positive bias of R1b (and possibly others like R1a, some subclades of J2 or E1b1b) and the negative bias of G2a (and possibly many subclades of F, I, J1xJ1c3, and T), it would in fact take much less than a 1% bias in each direction for frequencies for shift dramatically since the Neolithic or Bronze Age.
Each mutation on the Y-chromosome can potentially increase or decrease the proportion of male offspring. I believe that this is how some haplogroups or subclades become numerically dominant in the long run, while others progressively disappear. Most mutations have no effect at all. That is why, once a mutation increasing the chances of having more male children, and therefore increasing the chances of survival of the Y-chromosome itself, takes place, the lineage can develop many new subclades without being affected positively or negatively. Some new subclades will eventually get even more positive mutations, while others will go back to a more stable male-female ratio.
I wouldn't be surprised if haplogroup G suffered such a disadvantage at first, at least until one of the mutations around G2a3b or G2a3b1 happened, which stimulated the growth of that particular branch. Likewise, widespread branches of hg I, like I1 and I2a1b (M423) probably owe some of their success to mutations conferring a slight bias towards more male offspring. Such a bias would be almost imperceptible in genealogical times (within a few generations), but significant over hundreds of generations.
In modern Palestine, haplogroup J1 makes up about 40% of the lineages, twice more than among the Jewish community. Since J1 is strongly associated with the Arabic expansion, it is reasonable to assume that at least a fifth of the lineages in the region were taken over by the Arabs. The Arabs surely also carried haplogroups E1b1b and T, common on the Red Sea coast of Arabia, and which are slightly higher among Palestinians than among the Jews. So we could assume that approximately 25% of Palestinian lineages today came with the Arabs during the Muslim conquest.
It makes sense when looking at other haplogroups like J2 and R1b, but it still doesn't explain the sharp drop experienced by haplogroup G from 10-15% to 3%. It could be that G was considerably more common among the Jews of the diaspora, which caused a sort of founder effect.
But then why was G so ubiquitous in all Neolithic sites tested so far ? Europe has been affected as much by the sharp decline of G as the Levant. What other factors could have caused a gradual decrease of G since the Neolithic ? Were G men more frequently the victims of foreign invasions because they had settled the fertile Mediterranean lands first ? Each invasion in the last 9000 years would have progressively reduced the proportion of the original Neolithic farmers as new people settled in. But then why hasn't E1b1b, which also spread agriculture from the Neolithic Levant, undergone the same decline ?
Another possibility is that the G Y-chromosome produces slightly less male offspring than other haplogroups. I theorised five years ago that the exceptionally wide distribution of haplogroup R1b (and in fact also R1a) was due in part to a genetic bias towards producing slightly more male children. It doesn't take much to achieve this over hundreds of generations. If haplogroup R1 produced just 1% more boys than other haplogroups in average, R1 would increase its proportion 7.4 folds after the roughly 200 generations since the presumed arrival of R1b in Western Europe 6000 years ago.
In other words, if a population was composed of 100 R1b men and 100 men belonging to other haplogroups, if R1b men fathered 101 boys each generation, but other haplogroups kept a stable 100, it would take only 70 generations (about 2000 years) for R1b men to reach 200 boys born each generation, and therefore double their proportion against other haplogroups. The R1b frequency would thus pass from 50% to 66.6%. After 200 generations (about 6000 years), there would be 738 R1b boys against 100 other boys born at each generation. R1b would now make up 88% of the lineages in that population. As you can see a very minor initial advantage can lead to enormous changes in frequencies after a few millennia. Western Europe now has about 60% of R1b in average. With a bias of 1% more boys per generation, it would have taken an initial population of less than 10% of R1b 6000 years ago to reach that modern proportion.
If haplogroup G had the opposite bias, and produced 1% less boys than men belonging to other haplogroups, its proportion would gradually decline without any other factor required. If a given Neolithic population had 50% of hg G, with a bias of -1% of boys per generation against other haplogroups, it would have taken about 7000 years for the proportion of G to naturally decline to only 5% of the population.
If we combine both the positive bias of R1b (and possibly others like R1a, some subclades of J2 or E1b1b) and the negative bias of G2a (and possibly many subclades of F, I, J1xJ1c3, and T), it would in fact take much less than a 1% bias in each direction for frequencies for shift dramatically since the Neolithic or Bronze Age.
Each mutation on the Y-chromosome can potentially increase or decrease the proportion of male offspring. I believe that this is how some haplogroups or subclades become numerically dominant in the long run, while others progressively disappear. Most mutations have no effect at all. That is why, once a mutation increasing the chances of having more male children, and therefore increasing the chances of survival of the Y-chromosome itself, takes place, the lineage can develop many new subclades without being affected positively or negatively. Some new subclades will eventually get even more positive mutations, while others will go back to a more stable male-female ratio.
I wouldn't be surprised if haplogroup G suffered such a disadvantage at first, at least until one of the mutations around G2a3b or G2a3b1 happened, which stimulated the growth of that particular branch. Likewise, widespread branches of hg I, like I1 and I2a1b (M423) probably owe some of their success to mutations conferring a slight bias towards more male offspring. Such a bias would be almost imperceptible in genealogical times (within a few generations), but significant over hundreds of generations.
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. If it is true then good job, but all i see is a lot of story telling and little reliance on what the scientific community has proven. Any professionally done scientific study that you can provide me with that will show some proof to what you are saying will be great.
